Syphilis can cause mental disorders. If syphilis is left untreated and progresses to stage 3 syphilis, it can lead to neurological changes that can cause abnormal behaviour and manifest as symptoms of psychosis. However, if a patient has no manifestations of syphilis, or if syphilis is not diagnosed on examination, and a psychotic disorder develops, the first consideration should be other psychiatric disorders or the effects of a socially stressful event.